docs: add CI badge to README

Author: ancongui

README.md

@@ -1,5 +1,7 @@
 # Firefly Common Data Library
 
+[![CI](https://github.com/fireflyframework/fireflyframework-data/actions/workflows/ci.yml/badge.svg)](https://github.com/fireflyframework/fireflyframework-data/actions/workflows/ci.yml)
+
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](LICENSE)
 [![Java](https://img.shields.io/badge/Java-21+-orange.svg)](https://openjdk.java.net/)
 [![Spring Boot](https://img.shields.io/badge/Spring%20Boot-3.x-brightgreen.svg)](https://spring.io/projects/spring-boot)